The present invention relates to a twin-crank type heat engine comprising two symmetrically arranged crank shafts with power elements made of a shape memory metal having the most effective mechanical properties, in order to generate mechanical energy by optimum rotation of said crank shafts.
As examples of a conventional engine using a shape memory metal to convert thermal energy into mechanical energy, generally, offset type, swash plate type, or belt type engines have been previously well-known. Due to the contradiction of mechanism, however, these engines have not been in use for practical purposes.
In case of the offset-crank type engine, a coil-shaped power element is gradually submerged from the front part thereof into hot water. Due to such gradual submergence of the power element, a thermal tensile force generated by the first submerged part of coil is consumed to lengthen the following part, thereby causing the amount of power loss to increase. Moreover, less than twenty percent of the tensile force is effective to generate the rotating power.
In the swash-plate type engine, maximum efficiency can be obtained at the slope angle of 45.degree.. Even in this condition, however, only seventy percent (70%) of the thermal tensile force (Sin 45.degree.=0.7070) is effective, thereby causing the power loss to be more than thirty percent (30%).
In the belt type engine, the power element is formed into a belt associated with a pulley. The pulley is driven by the friction created by the thermal tensile force. Accordingly, the obtained effective power is limited by the value of the friction coefficient. Moreover, direct contact between the power element and the pulley causes an adverse effect by reducing the service life of belt. In addition, a heat exchange between the power element and the pulley is insufficiently carried out at contact regions while heating and cooling are applied.